Re: K calculations

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-uswest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
> 
> Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<Parpp807-at-aol-dot-com>
> 
> In a message dated 2/15/01 12:48:59 PM Central Standard Time,
> tesla-at-pupman-dot-com writes:
> 
> << Sorry, but it just isn't that simple.  Your approximate formula for the
>  inductance of a solenoid is just that, and accurate over a limited range
>  of R/H.  There is a way to calculate the coupling for two concentric
>  coaxial coils of the same diameter, but that isn't the way most TC's are
>  built.
> 
>  Ed
>   >>
> Ed,
> See the appendix pages of Terman for the empiracly derived formulas for
> helical coils
> of various configurations.
> 
> Ralph Zekelman

	The formulae in Terman's appendix (Appendix A, pp 795-796 of my second
edition (bought in 1944 while I was attending the University of
Illinois) are NOT empirical.  They are from a Bureau of Standards
Bulletin of about 1906 (have a photocopy, but not where I can check the
exact date), reproduced in the famous Circular 74 circa 1918, and
repeated in the texts of F.W. Grover.  Terman's expressions are
truncated versions of the general series expansion, "good enough for
government work".  If anyone is interested, I have a Q Basic program for
PC and a Quick Basic program for the Mac which perform these
calculations for coaxial solenoids of arbitrary dimensions.  They use
interpolation of the tables in Grover, and are probably good to about
0.1% for most geometries encountered in TC work.  10% would be plenty
close, of course, but I like to fool myself with all of those decimal
places!

	On Paul Nicholson's web site: 

	http://www.abelian.demon.co.uk/acmi/ 

he has a a less convenient (in my opinion) but considerably more general
program which handles conical and flat primaries, as well as solenoids. 
With these programs available I wouldn't bother to make hand
calculations.  The various inductance formulae are much simpler and
quite amenable to simple calculation.

Ed